This invention relates to the catalytic dewaxing of waxy component-containing hydrocarbon oils. It is especially directed to the preparation of lubricating oils having a high viscosity index, a high 650.degree. F.+ yield and reduced pour and cloud points.
Refining suitable petroleum crude oils to obtain a variety of lubricating oils which function effectively in diverse environments has become a highly developed and complex art. Although the broad principles involved in refining are qualitatively understood, the art is encumbered by quantitative uncertainties which require a considerable resort to empiricism in practical refining. Underlying these quantitative uncertainties is the complexity of the molecular constitution of lubricating oils. Because lubricating oils for the most part are based on petroleum fractions boiling above about 450.degree. F., the molecular weights of the hydrocarbon constituents are high and these constituents display almost all conceivable structure types. This complexity and its consequences are referred to in well-known treatises, such as, for example, "Petroleum Refinery Engineering" by W.L. Nelson, McGraw-Hill Book Company, Inc., New York, NY 1958 (4th Ed.).
In general, the basic premise in lubricant refining is that a suitable crude oil, as shown by experience or by assay, contains a quantity of lubricant stock having a predetermined set of properties, such as, for example, appropriate viscosity, oxidation stability and maintenance of fluidity at low temperatures. The process of refining to isolate that lubricant stock consists of a set of subtractive unit operations which removes the unwanted components. The most important of these unit operations includes distillation, solvent refining and dewaxing which are basically physical separation processes in the sense that if all of the separated fractions were to be recombined, the crude oil would be reconstituted.
A refined lubricant stock can be used by itself or it can be blended with another refined lubricant stock having different properties. The refined lubricant stock prior to use as a lubricant can also be compounded with one or more additives which function, for example, as antioxidants, extreme pressure additives, V.I. improves, and the like.
For the preparation of a high grade distillate lubricating oil stock, the current practice is to vacuum distill an atmospheric tower residuum from an appropriate crude oil as the first step. This step provides one or more raw stocks within the boiling range of from about 450.degree. to about 1050.degree. F. After preparation of a raw stock of suitable boiling range, it is extracted with a solvent, e.g., furfural, phenol, sulfolane or chlorex, which is selective for aromatic hydrocarbons and which removes undesirable components. The raffinate from solvent refining is then dewaxed, for example, by admixing with a solvent, e.g., a blend of methyl ethyl ketone and toluene. The mixture is chilled to induce crystallization of the parafin waxes which are then separated from the raffinate. Sufficient quantities of wax are removed to provide the desired pour point for the raffinate.
Other known and conventional processes such as hydrofinishing or clay percolation can be used if needed to reduce the nitrogen and sulfur content or improve the color of the lubricating oil stock.
Viscosity index (V.I.) is a quality parameter of considerable importance for distillate lubricating oils to be used in automotive engines and aircraft engines subject to wide variations in temperature. This index indicates the degree of change of viscosity with temperature. A high V.I., e.g., one of at least about 85, indicates an oil which resists the tendency to become excessively viscous at low temperature or excessively thin at high temperatures. Measurement of the Saybolt Universal Viscosity of an oil at 100.degree. and 210.degree. F. and referral to correlations provides a measure of the V.I. of an oil. For purposes of the present invention, whenever V.I. is referred to, the V.I. as noted in the Viscosity Index tabulations of ASTM D567 published by ASTM, or equivalent, is intended.
The dewaxing mechanism of catalytic hydrodewaxing is different from that of solvent dewaxing resulting in some differences in chemical composition. Catalytically dewaxed products produce a haze on standing at 10.degree. F. above specification pour point for more than twelve hours--known as Overnight Cloud (ONC) formation. The extent of this ONC formation is less severe with solvent dewaxed oils. Although such an ONC formation does not affect the product quality of catalytically dewaxed oils, it is beneficial to reduce the Overnight Cloud (ONC) formation since in some areas of the marketplace any increase is considered undesirable.
In recent years, catalytic techniques have become available for the dewaxing of petroleum stocks. A process of that nature developed by British Petroleum is described in The Oil and Gas Journal, dated Jan. 6, 1975, at pages 69-73. See also U.S. Pat. No. 3,668,113.
U.S. Pat. Reissue No. 29, 398 (of original U.S. Pat. No. 3,700,585) describes a process for catalytic dewaxing with a catalyst comprising zeolite ZSM-5. Such a process combined with catalytic hydrofinishing is described in U.S. Pat. No. 3,894,938.
U.S. Pat. No. 3,755,138 describes a process for mild solvent dewaxing to remove high quality wax from a lube stock which is then catalytically dewaxed to specification pour point.
U.S. Pat. No. 3,956,102 is directed to a process for the hydroewaxing of petroleum distillates utilizing a ZSM-5 type zeolite catalyst.
U.S. Pat. No. 4,053,532 is directed to a hydrodewaxing operation involving a Fischer-Tropsch synthesis procut utilizing ZSM-5 zeolite.
U.S. Pat. No. 4,247,388 describes dewaxing operations utilizing ZSM-5 type zeolites of specific activity.
U.S. Pat. No. 4,222,855 describes dewaxing operations to produce lubricating oils of low pour point and high V.I. utilizing zeolites including ZSM-23 and ZSM-35. U.S. Pat. No. 4,372,839 describes a method for dewaxing crude oils of high wax content by contacting the oils with two different zeolites, e.g., ZSM-5 and ZSM-35.
U.S. Pat. Nos. 4,419,220, 4,501,926 and 4,554,065 each describes a dewaxing process utilizing a zeolite Beta catalyst.
U.S. Pat. No. 4,541,919 describes a dewaxing process which utilizes a selectively coked large pore zeolite such as zeolite X, Y or Beta as catalyst.
The modification of zeolites by exchange and similar technology with large cations such as N.sup.+ and P.sup.+ and large branched compounds such as polyamines and the like is described in U.S. Pat. No. 4,101,595. Bulky phenolic and silicating zeolite surface-modifying agents are described in U.S. Pat. Nos. 4,100,215 and 4,002,697, respectively. As disclosed in U.S. Pat. Nos. 4,520221 and 4,568,786, zeolites which have been surface-deactivated by treatment with bulky dialkylamines are useful as catalysts for the oligomerization of lower olefins such as propylene to provide lubricating oil stocks.
As far as is known, surface-deactivated zeolites have heretofore not been known for use as hydrodewaxing catalysts.